Reciprocating saws are used to cut a variety of objects, such as metal pipes, wood and drywall. Such saws typically include a housing and a spindle mounted in the housing for reciprocating motion along an axis that is parallel to the longitudinal extent of the spindle. An electric motor provides power to the spindle through a mechanical reciprocating device that converts the rotary motion of a motor shaft to reciprocating motion of the spindle. Such mechanical reciprocating devices can, for example, include an eccentric drive, as disclosed in U.S. Pat. No. 5,079,844, or wobble plate drive, as disclosed in U.S. Pat. Nos. 5,025,562 and 5,050,307.
In addition to various types of drive mechanisms, there are also various types of reciprocating motion. For example, the simplest type is straight linear motion, in which the spindle and blade are translated along a linear path parallel to the spindle and returned along the same path. Alternatively, rocking motion is motion in which the spindle and blade are translated and returned along a path oblique to the spindle axis. Such motion may be straight or curved, and may help to drive the saw blade into the workpiece on the cutting stroke and retract the blade on the return stroke. As another alternative, orbital motion is motion in which the spindle and saw blade are translated along a cutting path and returned along a different path. Typically, the paths form a loop-type movement that forces the saw blade into the workpiece on the cutting stroke and then lifts the saw blade off the workpiece on the return stroke. All of these types of movement involve some reciprocation of the saw blade and are therefore considered to be a form of reciprocating motion.
The reciprocating motion of the spindle, and other components attached to the spindle such as the saw blade and drive components, causes vibration of the saw. Such vibration makes relative positioning of the saw to the work piece difficult, and can be significant in the case of hand held saws. Therefore, it is known to use a counterbalance that provides an inertial force opposed to the primary reciprocating inertial force. For example, in U.S. Pat. No. 5,025,562 issued Jun. 25, 1991 to Palm, a reciprocating saw is disclosed including a counterbalanced reciprocating drive having a jack shaft on which primary and secondary wobble plates are mounted. The primary wobble plate drives the spindle, and the secondary wobble plate drives a mass in a direction opposed to the spindle movement.